Syncing action and lips of a charecter with pre recorded voice over
There are a few approaches you can try. I would first enable Simplify to make the scene a little lighter while you're animating.

Another way to make your animations run faster is to split up the blend file into multiple files, and use them as linked libraries. You'd have one file with the rigged character model, another one with the scene, and a third one with the animation data. You can then link the rigged character into the animation file, make a local proxy of the armature, and animate the character. Because the animation file doesn't contain the rest of the scene, your computer will have an easier time moving from frame to frame. Once you have the animation the way you want it, you can link the animated character into the scene for lighting &amp; rendering.